Synthesis of Oppositely Charged Block Copolymers of Poly(ethylene glycol) via Reversible Addition−Fragmentation Chain Transfer Radical Polymerization and Characterization of Their Polyion Complex Micelles in Water

Diblock copolymers consisting of a water-soluble nonionic block and either an anionic or cationic block were prepared from sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) or (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTAC) via reversible addition−fragmentation chain transfer (RAFT)-controlled radical polymerization using poly(ethylene glycol) (PEG)-based chain transfer agent (PEG-CTA) in water. The RAFT polymerization proceeded in a living fashion, as suggested by the observation that the number-average molecular weight (Mn) increased linearly with the monomer conversion (up to conversions of 30% for MAPTAC and 50% for AMPS), whereas the polydispersity (Mw/Mn) remained nearly constant (Mw/Mn b-PAMPS and PEG-b-PMAPTAC, led to the spontaneous formation of polyion complex (PIC) micelles. The PIC micelles were characterized by 1H NMR spin−spin relaxation time, static light scattering (SLS), dynamic light scattering (DLS), and scanning electron microscopy (SEM) techniques. The hydrodynamic size of the micelle depended on the mixing ratio of PEG-b-PAMPS and PEG-b-PMAPTAC with the size maximizing at the mixing ratio of stoichiometric charge neutralization. The mixing of the oppositely charged diblock copolymers with shorter charged blocks formed a core−shell PIC micelle. In contrast, a complicated aggregate was formed from a pair of longer blocks. The exact structure of the aggregate is still an open question, but it is speculated to be a multicore intermicellar aggregate on the basis of various characterization data

Physicochemical Properties of Micelles of Poly(styrene-<i>b</i>-[3-(methacryloylamino)propyl]trimethylammonium chloride-<i>b</i>-ethylene oxide) in Aqueous Solutions

Polymeric micelles from a new triblock copolymer, polystyrene-block-poly[(3-(methacryloylamino)propyl)trimethylammonium chloride]-block-poly(ethylene oxide) (PS-b-PMAPTAC-b-PEO), were prepared in aqueous solutions and characterized by various techniques including dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. The micelle consists of a PS core, PMAPTAC shell, and PEO corona. It was revealed by SEM and DLS measurements that the micelles have a spherical structure with a hydrodynamic diameter about 75 nm. The addition of tungstate to the micellar solution caused a morphological change in the micelles from extended to shrunken spheres, which can be attributed to the fact that electrostatic repulsion among the cationic PMAPTAC blocks is canceled by the negative charge of the bound tungstate ions. Effective incorporation of tungstate ions into the micelles were confirmed by TEM and ζ-potential measurements

Synthesis of Hollow CaCO₃ Nanospheres Templated by Micelles of Poly(styrene-<i>b</i>-acrylic acid-<i>b</i>-ethylene glycol) in Aqueous Solutions

An asymmetric triblock copolymer, poly(styrene-b-acrylic acid-b-ethylene glycol) (PS-b-PAA-b-PEG), was synthesized via reversible addition−fragmentation chain transfer controlled radical polymerization. Micelles of PS-b-PAA-b-PEG with PS core, PAA shell, and PEG corona were then prepared in aqueous solutions, followed by extensive characterization based on dynamic light scattering, zeta-potential, and transmission electron microscopy (TEM) measurements. The well-characterized micelles were used to fabricate hollow nanospheres of CaCO3 as a template. It was elucidated from TEM measurements that the hollow nanospheres have a uniform size with cavity diameters of ca. 20 nm. The X-ray diffraction analysis revealed a high purity and crystallinity of the hollow nanospheres. The hollow CaCO3 nanospheres thus obtained have been used for the controlled release of an anti-inflammatory drug, naproxen. The significance of this study is that we have overcome a previous difficulty in the synthesis of hollow CaCO3 nanospheres. After mixing of Ca2+ and CO32− ions, the growth of CaCO3 is generally quite rapid to induce large crystal, which prevented us from obtaining hollow CaCO3 nanospheres with controlled structure. However, we could solve this issue by using micelles of PS-b-PAA-b-PEG as a template. The PS core acts as a template that can be removed to form a cavity of hollow CaCO3 nanospheres, the PAA shell is beneficial for arresting Ca2+ ions to produce CaCO3, and the PEG corona stabilizes the CaCO3/micelle nanocomposite to prevent secondary aggregate formation